A water pump for a vehicle is adapted to pressurize and transmit cooling water to an engine, so that the cooling water is circulated in the engine and the heat of the engine is thus released. In the same manner as a compressor of an air conditioner, the water pump is activated by the rotary power applied from the engine. That is, the water pump is generally operated together with the activation of the engine, thereby supplying the cooling water to the engine.
FIG. 1 is an exploded perspective view showing a power transmission device for a water pump in a conventional practice, wherein the conventional power transmission device for a water pump includes a pulley 60 adapted to receive the rotary power of an engine through a belt mounted thereon.
The pulley 60 has a field coil assembly-mounting space 64 formed on one side surface (on the right side in the drawing) so as to mount a field coil assembly 50 into which a field coil 51 is embedded thereon. The pulley 60 also has a moving space 69 formed on the opposite side to the field coil assembly-mounting space 64, in which a disk 70 is movably mounted.
If power source is applied to the field coil 51, the disk 70 is moved to the pulley 60 by means of an attracting magnetic flux generated from the field coil 51 and is thus separated from a hub assembly 80. Contrarily, if the power source applied to the field coil 51 is removed, the disk 70 is returned to its original position and is thus coupled to the hub assembly 80.
A resilient member 74 attached to the periphery of the disk 70 is fixed to the moving space 69 of the pulley 60 to apply a resilient force to the disk 70, so that the disk 70 is brought into close contact with the hub assembly 80. When the disk 70 is moved to the pulley 60 by means of the generation of the attracting magnetic flux, resilient deformation occurs around the periphery of the resilient member 70 fixed to the pulley 60, so that the disk 70 is separated from the hub assembly 80.
The disk 70 has a plurality of rivets 76 coupled thereto in such a manner as to be protruded toward the hub assembly 80. The rivets 76 have interlocking grooves 77 formed at the front ends thereof, and the interlocking grooves 77 are lockedly coupled to interlocking protrusions 84 formed on the side surface of an interlocking plate 82 of the hub assembly 80. Each interlocking groove 77 has a shape corresponding to each interlocking protrusion 84, and as the interlocking groove 77 is lockedly fitted to the interlocking protrusion 84, the disk 70 and the hub assembly 80 can be rotated together.
The hub assembly 80 has a hub 86 disposed at the center thereof, and the hub 86 has the rotary shaft for driving the water pump press-fitted thereto, so that the hub 86 rotates as the rotary shaft rotates.
According to the conventional power transmission device for the water pump under the above-mentioned configuration, if power source is applied to the field coil 51, the field coil 51 generates the attracting magnetic flux therefrom, which is applied to the disk 70 and exceeds the resilient force of the resilient member 74, so that the disk 70 is moved to the pulley 60 within the moving space 69. Accordingly, the lock fitting between the rivets 76 and the interlocking protrusions 84 is released, and the disk 70 is thus separated from the hub assembly 80. Even though the pulley 60 is rotated by means of the power applied from the engine, therefore, the power is not transmitted to the rotary shaft mounted on the hub assembly 80, and thus, the cooling water is not supplied to the engine.
So as to supply the cooling water to the engine, the application of the power to the field coil 51 shuts off. As a result, the attracting magnetic flux is not generated from the field coil 51, and the disk 70 is moved to the direction being distant from the pulley 60 within the moving space 69 by means of the resilient force of the resilient member 74. Accordingly, the interlocking grooves 77 of the rivets 76 are lockedly fitted to the interlocking protrusions 84 of the hub assembly 80, and thus, the hub assembly 80 is coupled to the disk 70, thereby being rotated together with the disk 70. Furthermore, an impeller coupled to one end of the hub assembly is rotated together with the rotary shaft, thereby supplying the cooling water to the engine.
Like this, if the power transmitted from the pulley 60 to the disk 70 is regulated through the application of the power source to the field coil 61 or the shut-off of the application of the power source, the power regulation can be performed rapidly and accurately, and at the same time, the rotation synchronization can be achieved at a high speed and stably.
According to the conventional power transmission device for a water pump, however, some problems occur when the interlocking grooves 77 of the rivets 76 of the disk 70 are lockedly fitted to the interlocking protrusions 84 on the interlocking plate 82 of the hub assembly 80. Through the movement of the disk 70 toward the hub assembly 80, in more detail, when the rivets 76 being rotated are brought into contact with the interlocking plate 82 being in a stop state, the interlocking grooves 77 should be lockedly fitted to the interlocking protrusions 84 in a reliable manner, but the lock fitting is not carried out momentarily and accurately, thereby making the synchronization typically delayed. In this process, the interlocking grooves 77 and the interlocking protrusions 84 have just matching coupling to each other, thereby generating abnormal noises during the lock fitting process and causing the wearing and damage on the interlocking grooves 77 and the interlocking protrusions 84. These problems undesirably make the reliability in the operation of the power transmission device deteriorated badly.